Lori,
The basic rule for laptops, batteries, and DVD play times is: your mileage will vary. I travel a lot, I get a new laptop about every 12 months, and I've seen significant variances between different brands. The good news is, there is plenty of time between now and the cruise for you to experiment and see what kind of play time you get.
Of course, the bad news is, there is plenty of time between now and the cruise. Crud!!!
You can also try contacting your airline and find out if they have power outlets on board, and if so, what kind of adapter you need to use them (they're almost never regular US-style plugs). I fly American when I travel, and almost all of their planes have them. I have an adapter so that battery power is never an issue, which is important to me since my trips are usually to far-away places like NY, London, Amsterdam, etc. Usually, these adapters are considerably less expensive than additional batteries or portable DVD players.
Sara, you're right, this is gonna be fun!!! With the West Coast itinerary, this is quite different from the normal cruises: with so many people from California going, it gives us a great chance to meet up before-hand (referring to an earlier post, you'll know before getting on the ship whether we're "dreadful"!!). That wasn't really possible with Port Canaveral-based cruises.
Amy, thanks for the recommendations. These sound yummy.
Is it Friday yet?
Chris